1. Field of the Invention
The present invention relates to novel compositions of matter, and especially aqueous emulsions thereof, which comprise organosilicic polymers together with organic polymers. The subject compositions can be employed for the production of anti-adhesive (non-stick) and/or water-repellent coatings on various substrates (supports), in particular on cellulosic materials.
2. Description of the Prior Art
Compositions which are in the form of aqueous emulsions (hereinafter designated "aqueous emulsion compositions") containing organosilicic polymers, either alone or admixed with various organic compounds or polymers, have long been known to this art. Compare, in particular, published Japanese Application No. 72/23,325, U.S. Pat. Nos. 4,127,460 and 4,288,356 and French Pat. Nos. 2,401,195 and 2,419,961.
Japanese Application No. 72/23,325 describes a composition containing a diorganopolysiloxane oil blocked at each end of its polymer chain with a hydroxy radical bonded to a silicon atom, a methylhydropolysiloxane, a carboxymethylcellulose, a monoether of a polyalkylene glycol, a surface-active agent, a tin salt such as dibutyltin dilaurate and water.
This composition is easily spread onto papers coated with polyolefins and provides a friction-resistant coating.
U.S. Pat. No. 4,127,460 describes a composition containing an alkylhydropolysiloxane, a liquid polyacrylate-containing tertiary amine, at least partially neutralized with an acid, a photosensitizer, an emulsifying agent and water. This composition hardens on exposure to ultraviolet radiations; the resultant coating adheres efficiently to the surface of supercalendered papers.
French Pat. No. 2,401,195 relates to a composition incorporating a diorganopolysiloxane having a viscosity of 50,000 to 500,000 mPa.s at 25.degree. C., blocked at each end of its polymer chain with a hydroxy radical bonded to a silicon atom, containing from 0.1 to 4% by weight of vinyl radicals bonded to the silicon atoms in its polymer chain, or a diorganopolysiloxane of the same type but blocked at each end of its polymer chain with a diorganovinylsiloxy unit, an organohydropolysiloxane, a colloidal silica, an emulsifying agent, a catalytic amount of a platinum derivative and water.
Once it is deposited onto a paper substrate, this composition is converted by heating into a coating, the anti-adhesive nature of which is improved in respect of contact adhesives.
Published French Application No. 2,419,961 relates to a composition comprising a liquid diorganopolysiloxane, having a viscosity of 1,500 to 24,000 mPa.s at 25.degree. C., blocked at each end of its polymer chain with a hydroxy radical bonded to a silicon atom, preferably containing from 0.1 to 2% by weight of vinyl radicals bonded to silicon atoms in its polymer chain, an organohydropolysiloxane, one or more emulsifying agents, a catalyst selected from among platinum derivatives and tin salts of carboxylic acids, and water.
In the case where tin salts are employed as catalysts for hardening, it is necessary to use a 3-component system respectively containing the hydroxylated diorganopolysiloxane emulsion, the organohydropolysiloxane emulsion and the tin salt emulsion. These three emulsions are mixed only at the point in time of use. The '961 publication also describes that the hydroxydiorganosiloxane emulsion employs a polyvinyl alcohol as an emulsifying agent and the organohydropolysiloxane emulsion employs a polyoxyethylenated alkylphenol.
This composition can harden either when cold or hot.
U.S. Pat. No. 4,288,356 relates to an aqueous emulsion which provides an elastomeric coating after deposition onto a substrate such as paper. This emulson is formed by mixing:
(i) an aqueous emulsion of a diorganopolysiloxane blocked at each end of its polymer chain with a hydroxy radical bonded to a silicon atom, having a molecular weight of at least 5,000, prepared by emulsion polymerization in the presence of an anionic catalyst;
(ii) an aqueous emulsion, also prepared by emulsion polymerization of a mixture of vinyl unsaturated monomers consisting of 1 to 7% by weight of an organosilicic monomer such as vinyltriethoxysilane and 93 to 99% by weight of an organic monomer such as styrene, methyl methacrylate, or vinyl chloride;
(iii) an aqueous emulsion of an organotin salt; and
(iv) a silane containing hydrolyzable groups functioning as a cross-linking agent, such as methyltrimethoxysilane.
The '356 patent teaches that it is essential that the mixture of the three emulsions be neutral or slightly basic before the silane containing the hydrolyzable groups is introduced.
Thus, the state of this art is that it is indeed possible to provide anti-adhesive coatings of good quality on numerous substrates, and in particular on cellulosic materials, from compositions which are in the form of aqueous emulsions and which contain organopolysiloxane polymers and optionally organic polymers.
The state of this art, however, is conspicuously silent as regards any specific means necessary to prepare an aqueous emulsion composition, stable to storage and to shear, conjointly containing a diorganopolysiloxane terminated at each end of its polymer chain by a SiOH radical, an organohydropolysiloxane, and an organic polymer. Moreover, over the course of the application of an aqueous emulsion composition to the surface of a substrate to be treated, this art is also silent as regards:
(1) the means to be employed to restrict or even prevent the penetration of the aqueous emulsion composition into the bulk of porous materials such as cellulosic materials;
(2) the means to be employed to prevent excessively fast evaporation of the water in the emulsion (water removal which is badly controlled occasionally gives rise to the formation of heterogeneities in the anti-adhesive coating produced);
(3) the means to be employed to prepare aqueous emulsion compositions which make it possible to impart both water-repellent and anti-adhesive properties (directly on papermaking machines) to unbleached, coarsely beaten papers (such papers still contain not insignificant quantities of products which inhibit sensitive catalysts for hardening such as platinum derivatives); and
(4) the means to be employed to obtain, from aqueous emulsion compositions, coatings which retain water-repellent and anti-adhesive properties at the same time, over a wide temperature region ranging, for example, from -100.degree. C. to 300.degree. C. Very low temperatures can be encountered in refrigeration equipment employed for deep-freezing foodstuffs, and very high temperatures in microwave ovens employed for fast cooking of foodstuffs. When the foodstuffs are wrapped in paper, it is essential that the latter not only withstands these rigorous treatments, but also, after the foodstuffs have returned to ambient temperature, has sufficient anti-adhesive characteristics to be removed from around the foodstuffs without tearing.
Hereinafter, all parts or percentages are by weight, unless otherwise indicated.